(1) Field of the Invention
The present invention relates to printed wiring boards and, more particularly, to a printed wiring board with zones of controlled thermal coefficient of expansion.
(2) Background Art
Printed wiring boards possessing a controlled thermal coefficient of expansion are very well known to those skilled in the art. In this regard, U.S. Pat. No. 3,794,887 to Brennan et al. teaches a printed circuit board including a plurality of flexible metal webs secured to a frame at their ends. A printed wiring board is secured to the webs so that each web has a free length between the frame and the adjacent edge of the printed wiring board. The webs provide a thermal path and isolation from vibration as well as a electrical path to the printed wiring board.
U.S. Pat. No. 4,318,954 to Jensen teaches a composite printed wiring board including a surface fabricated from fiber of glass reinforced epoxy laminates secured by means of thermal set adhesive to a support member which is fabricated from graphite film and reinforced thermal set resin having a low coefficient of thermal expansion approaching zero. The unrestrained coefficient of thermal expansion of the printed wiring board is significantly greater than that of the support member. However, the composite assembly possesses a thermal expansion coefficient greatly reduced from that of the glass fiber reinforced epoxy and approaching that of a ceramic chip carrier.
U.S. Pat. No. 4,495,378 to Dotzer et al. teaches a circuit board consisting of a flat core plate of metallic material, graphite or electrically conductive carbon with a coating of electroplated aluminum eloxal. A conductor run structure may be generated on the aluminum eloxal layer to provide circuit interconnections.
U.S. Pat. No. 4,496,793 to Hanson et al. teaches a multilayer circuit board laminate which includes one or more stabilizing metal sheets for reducing the thermal coefficient of expansion of the laminate. The circuit board laminate disclosed is particularly useful in conjunction with leadless components and incorporates one or more stabilizing metal sheets into the composite multilayer board laminate assembly to stabilize the laminates thermal coefficient of expansion thereby enabling the laminate to be used in conjunction with leadless electronic components. The stabilizing layer may be formed of a composite metal dielectric laminate enabling the layer to be provided with a noncontinuous floating type pattern.
The above cited art while teaching various methods of controlling thermal coefficient of expansion and variously removing heat generated by electronic components, is not seen to teach the use of a stabilizing layer to control thermal coefficient of expansion and to remove heat in the manner taught by the present invention.